1. Field of the Invention
This invention relates to a method of depositing a metal on a surface and more particularly, to a method of selectively depositing an electroless metal deposit on a surface.
2. Discussion of the Prior Art
Heretofore, it has been known to employ a number of pretreatment or sensitization baths in effecting the electroless deposition of metals on various surfaces. Typically, such prior art sensitization baths used commercially have been expensive because they depend upon a noble metal, e.g., Pd, Pt, Ag, Au, etc., as the sensitizing component. However, recently methods have been reported in which electroless metal deposits can be applied to a broad variety of insulating substrates without the need to use expensive noble metals but on the contrary, employ reducible salt compositions of non-noble metals. U.S. Pat. Nos. 3,772,056; 3,772,078; 3,907,621; 3,925,578; and 3,930,963 disclose such methods. A problem with the methods disclosed in these patents and not recognized or addressed thereby or therein is that of moisture or humidity which affects a catalytic real image formed by the methods and the resultant electroless metal deposit.
The above-described problem has been recognized and obviated by a process revealed in U.S. patent application Ser. No. 714,455, now U.S. Pat. No. 4,084,023, filed by R. V. Dafter, Jr. on Aug. 16, 1976, and entitled "A Method of Depositing a Metal on a Surface," and assigned to the assignee hereof. In this method the real image is treated with a fixing solution comprising an autocatalytic reducing agent, e.g. formaldehyde where the real image comprises a copper species. Although the real image after treatment with such a fixing solution is successfully stabilized with respect to ageing and/or high humidity conditions, it has been found that upon subsequent treatment with an electroless plating solution the resultant electroless deposit upon the real image becomes smeared and tends to spread or in general to degrade. This condition occurs with real images which have been stabilized with the fixing solution of the aforementioned Dafter application as well as with those real images which have not been treated or stabilized with the fixing solution, such as the real images obtained with the above-identified U.S. patents.
Accordingly, a method of preventing the smearing or spreading of an electroless metal deposit on the real image is needed and is an object of this invention.